In a photomechanical process where a continuous tone densities of an original are converted respectively into the group consisting of the halftone dots having the areas proportional to the density, a silver halide photographic light sensitive material (hereinafter referred simply to a light sensitive material) having a high contrast photographic characteristic is generally used.
For providing a high contrast characteristic to an image, a desired photographic light sensitive material has been prepared in such a manner as described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP OPI Publication) No. 56-106244/1981, U.S. Pat. No. 4,686,167 and European Patent No. 333,435; in which a compound such as hydrazine is contained as a nucleating agent into a silver halide photographic light sensitive material and silver halide grains capable of effectively displaying contrast-increasing characteristic of the compound are further used or other photographic additives are suitably used in combination. The silver halide photographic light sensitive materials such as those mentioned above are apparently proved to be stable as a light sensitive material and a high contrast photographic image can be obtained even when they are processed with a rapid processable developer.
However, if these photographic materials are used in the step of converting a continuous tone image to a halftone image, sandlike fog or black dot which is generally referred to pepper fog can occur in halftone dots, leading to impaired dot quality, particularly when enlarging a screen image. These are remarkable particularly after raw stock keeping. In an attempt at solving this problem, various stabilizers ot restrainers having hetero atom(s) have been added but this has not always proved to be a complete solution. Under these circumstances, a light sensitive material that uses an effective contrast increasing agent free from that problem is desired.
On the other hand, as one of the methods for forming a positive image with the use of a direct positive type silver halide photographic light sensitive material, there has been known a method for forming a positive image in which an unfogged internal latent image silver halide emulsion is used and, after imagewise exposed to light, is surface-developed in the presence of a foggant to form a positive image.
In the above-mentioned technical field, various techniques have been known so far. For example, these techniques include, typically, those described in U.S. Pat. Nos. 2,592,250, 2,456,957, 2,497,875 and 2,588,982, British Patent No. 1,151,363, JP Examined Publication No. 43-29405/1968, JP OPI Publication Nos. 47-9434/1972, 47-9677/1972, 47-32813/1972, 47-32814/1972, 48-9727/1973 and 48-9717/1973, U.S. Pat. Nos. 3,761,266 and 3,496,577 and JP OPI Publication Nos. 50-8524/1975 and 50-38525/1975.
Hydrazine compounds have been known so far as useful foggants. For example, the foggants applicable thereto include hydrazine compounds given in U.S. Pat. Nos. 2,563,758 and 2,588,982, naphthyl hydrazine sulfonic acid given in U.S. Pat. No. 2,064,700, and sulfomethyl hydrazines given in British Patent No. 1,403,018. Further, JP Examined Publication No. 41-17184/1966 describes that a color positive image is obtained by making use of a hydrazide or hydrazone compound.
However, when making use of the above-given compounds, the induction period before starting a development is rather longer than that in the development of an ordinary latent image. Therefore, the development turns out to be considerably delayed.
When the conventional techniques are applied to a multilayered color photographic light sensitive material, these techniques have had such a problem that the characteristics are liable to cause an ununiformity between the layers and the resulting maximum density becomes lower.
For obtaining an excellent result while keeping a desirable fogging function, a development has been carried out at a high pH of not lower than 12. However, this type of developments have not desirable at all, because the deterioration of a developing agent is seriously accelerated and the physical property of a layer of a photographic light sensitive material is deteriorated.
Further, it has not been desirable as for the storage stability of raw stock. Therefore, as for the direct-positive type silver halide photographic light sensitive materials, it has been demanded to provide a light sensitive material containing an advantageous foggant improved in the above-mentioned problems.